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Sea Floor Spreading

Fact: The tallest mountain on the planet is not Mt. Everest, which is only 29 028 ft. The tallest mountain in the world is actually Mauna Kea, in Hawaii, which is closer to 31 000 ft. You just can't see the two-thirds of the mountain that is under water.

Materials that can flow tend to lose thermal energy by the convection process. This explains circulation in a pot of water that is being heated from below in the same way it describes the cooling of the Earth.

Mantle Convection

Deep materials, hotter than their surroundings (and hence buoyant), would tend to flow upward. In approaching the cool surface of the Earth, the material would lose its thermal energy, cool and sink, having lost buoyancy.

The Earth has an invisible magnetic field. All free-floating magnets at the Earth’s surface point to magnetic north.

Iron-rich minerals crystallizing from molten rock will orient towards magnetic north when they cool below the Curie point, the temperature above which permanent magnetism is impossible (580oC for magnetite).

Thus lavas lock in the record of Earth’s magnetic field when they form.

Interestingly, the polarity of the magnetic field shifts every 0.5 - 1.0 Myr. That means rocks formed over time will record either ‘normal’ magnetic orientation (like today), or reversed. Since this is a global phenomenon, these changes can be used for global stratigraphic correlation.

Rock magnetism has two components: the direction of magnetic ‘pointing’ and the inclination of this with the Earth’s surface. Magnetic inclination goes from nearly horizontal at the equator to vertical at the magnetic pole.

Thus, magnetic records give an indication of where the rock was on the surface when it was magnetized.